New System for Measuring the Photochemical Ozone Production Rate in the Atmosphere

We have developed a new system for measuring photochemical ozone production rates in the atmosphere. Specifically, the system measures the net photochemical oxidant (O_x: the sum of ozone (O₃) and nitrogen dioxide (NO₂)) production rates (P-L(O_x)). Measuring O_x avoids issues from perturbations to the photostationary states between nitrogen oxides (NO_x) and O₃. This system has "reaction" and "reference" chambers. Ambient air is introduced into both chambers, and O_x is photochemically produced in the reaction chamber and not generated in the reference chamber. Air from the chambers is alternately introduced into an NO-reaction (NO: nitric oxide) tube to convert O₃ to NO₂, and then the O_x concentration is measured as NO₂ using a laser-induced fluorescence technique. P-L(O_x) was obtained by dividing the difference in O_x concentrations between air samples from the two chambers by the mean residence time of the air in the reaction chamber. In this study, the P-L(O_x) measurement system was characterized, and the current detection limit of P-L(O_x) was determined to be 0.54 ppbv h^-1 with an integration time of 60 s (S/N = 2), assuming an ambient O_x concentration of 100 ppbv. Field measurements of P-L(O_x) were conducted using the system at a remote forest location.